1. Field of the Invention
The present invention relates to an active filter that restrains a harmonic component in a power system.
2. Description of the Related Art
For example, as disclosed by JP-A-2005-245117, a conventional active filter generally employs a method of obtaining compensation current used to restrain a harmonic component by carrying out dq axis transformation to detected system current.
The active filter can restrain a current harmonic only at one particular frequency present in a power system and cannot remove harmonic noises other than a fundamental wave in a system where multiple unspecified harmonics exist.
In general, a large number of harmonics with different frequency components exist in a power system, and therefore the use of the conventional active filter can neither provide a sufficient compensation effect nor restrain voltage harmonics.
This can be a significantly critical disadvantage in consideration of how the affects of harmonic noises increase as future development of power electronics industries, expansion of distributed power sources, and increase in various kinds of harmonic sources in power systems.